Advanced Semiconductor-Electrocatalyst Systems for Photoelectrochemical Hydrogen Production in Microgravity Environments

Abstract

Efficient artificial photosynthesis systems follow the concept of the Z-scheme of natural photosynthesis. They are realized as catalyst- and surface-functionalized photovoltaic tandem devices [1,2] enabling photoelectrochemical water oxidation while simultaneously recycling CO2 and generating hydrogen as a solar fuel for storable renewable energy. The successful implementation of an efficient photoelectrochemical (PEC) water splitting cell is not only a highly desirable approach to solving the energy challenge on earth: an effective air revitalization system generating a constant flux of O2 while simultaneously recycling CO2 and providing a sustainable fuel supply is also essential for the International Space Station and long-term space missions, where a regular resupply from earth is not possible. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in microgravity environment, providing an alternative route to existing life support technologies for space travel [3]. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15mAcm-2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the electrocatalyst using shadow nanosphere lithography [4]. We show that shadow nanosphere lithography can be used as a prosperous tool to obtain desired catalyst nanostructures of high fidelity on a light-absorbing semiconductor surface with tunable optical properties showing significant advantages for photoelectrochemical hydrogen production in microgravity and terrestrial applications [5].